Macroinvertebrates from a first order stream at Mt Jumbong, Kangwon-do, was examined for their abundance and biomass. Sampling was done by using a pipe sampler (${phi}$ 20 cm) for 11occasions (n = 5) at 4${sim}$6 weeks intervals during November 1997 through October 1998. Water temperature and electronic conductivity of the study stream ranged $0;{sim};14^{circ}C$ and 15${sim}$25 ${mu}s$/cm, respectively. During the study, 53 insect taxa and 3 non-insect taxa were collected. Annual mean number of individuals (${pm}$1 SD) was 77741${pm}$69232${cdot}$m$^{-2}$ ${cdot}$yr$^{-1}$, being high in winter (${pm}$1 SD) (December: 171178${pm}$130468 $m^{-2}$) and low in summer (${pm}$ 1 SD) (June: 29872${pm}$13078 $m^{-2}$). Non-predatory subfamilies of Chironomidae and Nemoura sp. occupied 53.3% and 21.8% of annual abundance. Annual mean biomass was 10g${cdot}$m$^{-2}$${cdot}$yr$^{-1}$ in ash free dry weight (AFDW), being high in late winter (February: 16 gAFDW $m^{-2}$.) and low in summer (June: 3 gAFDW $m^{-2}$). Gammarus sp. represented 39.8% of the total biomass and was followed by non-predatory subfamilies of Chironomidae (15.2%) and Hydatohylax sp. (8.5%, Limnephilidae: Trichoptera). Since the non-predatory subfamilies of chironomidae were composed of many species, Nemoura sp. was the most abundant taxon. However, Cammarus sp. was surely the most important taxon to the functional aspects of this first order stream ecosystems.